A biological agent — also called bio-agent, biological threat agent, biological warfare agent, biological weapon, or bioweapon — is a bacterium, virus, protozoan, parasite, or fungus that can be used purposefully as a weapon in bioterrorism or biological warfare (BW). In addition to these living and/or replicating pathogens, biological toxins are also included among the bio-agents. More than 1,200 different kinds of potentially weaponizable bio-agents have been described and studied to date.
Biological agents have the ability to adversely affect human health in a variety of ways, ranging from relatively mild allergic reactions to serious medical conditions, including death. Many of these organisms are ubiquitous in the natural environment where they are found in water, soil, plants, or animals. Bio-agents may be amenable to "weaponization" to render them easier to deploy or disseminate. Genetic modification may enhance their incapacitating or lethal properties, or render them impervious to conventional treatments or preventives. Since many bio-agents reproduce rapidly and require minimal resources for propagation, they are also a potential danger in a wide variety of occupational settings.
The former US biological warfare program (1943-1969) categorized its weaponized anti-personnel bio-agents as either Lethal Agents (Bacillus anthracis, Francisella tularensis, Botulinum toxin) or Incapacitating Agents (Brucella suis, Coxiella burnetii, Venezuelan equine encephalitis virus, Staphylococcal enterotoxin B). In the next section ("List of biological and toxin agents of military importance") the military symbols for various weaponized agents are given; this nomenclature system began in the US and UK BW programs of World War II and continued as NATO nomenclature through the Cold War.
Since 1997, United States law has declared a list of bio-agents designated by the U.S. Department of Health and Human Services or the U.S. Department of Agriculture that have the "potential to pose a severe threat to public health and safety" to be officially defined as "select agents" and possession or transportation of them are tightly controlled as such. Select agents are divided into "HHS select agents and toxins", "USDA select agents and toxins" and "Overlap [i.e., both HHS and USDA] select agents and toxins".
The U.S. Centers for Disease Control and Prevention (CDC) breaks biological agents into three categories: Category A, Category B, and Category C. Category A agents pose the greatest threat to the U.S. Criteria for being a Category A agent include high rates of morbidity and mortality; ease of dissemination and communicability; ability to cause public panic; and special action required by public health officials to respond. Category A agents include anthrax, botulism, plague, smallpox, tularemia, and viral hemorrhagic fevers.
List of biological and toxin agents of military importance
^Headquarters, Departments of the Army, the Navy, and the Air Force, and Commandant , Marine Corps (17 July 2000), Field Manual: Treatment of Biological Warfare Casualties (Army FM 8-284/Navy NAVMED P-5042/Air Force AFMAN (I) 44-156/Marine Corps MCRP 4-11.1C), para 1-4 (pg 1-3).
^Additional Requirements for Facilities Transferring or Receiving Select Agents, Title 42 CFR Part 72 and Appendix A; 15 April 1997 (DHHS).